Aortic Stenosis
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Introduction
The three possible areas for aortic stenosis to occur are subvalvular or subaortic (occurs below the valve), valvular or aortic (occurs at the valve) and supravalvular (occurs after the valve).
The stenotic area causing the problem is a consequence of fibrous tissue on and around the aortic valve. A narrowing of the aortic outflow tract causes an increase in pressure and this increased pressure leads to left ventricular dilation and concentric hypertrophy as a means of maintaining sufficient cardiac output. The severity of stenosis determines the extent of hypertrophy. Hypertrophy of the myocardium leads to an increased oxygen demand and decreased diastolic filling and insufficient oxygen to meet the new needs of the hypertrophied left ventricle predisposes the animal to ventricular arrhythmias. There is also an increased risk of bacterial endocarditis in animals affected by this condition.
Signalment
This condition is common in dogs, especially the subvalvular lesions. Boxers usually have valvular stenosis. It is rare in cats, but if they are affected, usually they get supravalvular lesions.
Predisposed breeds include the Newfoundland, Boxer, German Shepherd, Golden Retriever and Bull Terrier.
Clinical Signs
As with all heart conditions, weakness, exercise intolerance, syncope, stunting of growth and pallor are all possible clinical signs. However, the disease may be asymptomatic.
Diagnosis
Clinical signs as well as history are indicative of a heart condition.
Upon physical examination a systolic murmur will be heard which is loudest over aortic valve and there may also be weak femoral pulses.
Radiographic findings may show left ventricular enlargement or bulge around the aortic valve, however, radiographs may appear normal due to concentric hypertrophy.
Electrocardiography (ECG) may show an increased R-wave amplitude (indicates left ventricular hypertrophy) or ventricular arrhythmias (only severely affected animals).
Echocardiography may show left ventricular concentric hypertrophy, fibrous tissue around aortic valve, dilation of the ascending aorta and dilation of the left atrium.
Treatment and Control
Palliative treatment is usually the treatment of choice. It will attempt to alleviate symptoms without curing disease. Methods include exercise restriction and beta-blockers (prevent/control ventricular arrhythmias).
Surgical treatment offers a poor outcome with current methods. One suggested surgery is a balloon valvuloplasty, though it has been performed only with limited efficacy.
Prognosis
In mild to moderate cases of the condition , there is usually a normal quality of life if there is no progression of the malformation. In severe cases, there is often a poor quality of life. Complications from development of congestive heart failure or cardiac arrhythmias can occur, as can sudden death within the first 1-3 years of life.
References
Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition), W.B. Saunders Company
Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2)W.B. Saunders Company
Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier